[Top] [All Lists]

Re: [ietf-smtp] test for port 25 of sending MTA - for spam detection

2013-08-23 06:46:11
The advantage over DNSBL is that for DNSBL you first need to register the 
site with DNSBL. The callback is instantaneous. And the call back function 
on circumstances that a spammer is not likely to control, such as port 
on a router, and allowing connections from outside to port 25. Apart from the 
spamer also
delivering a functional MTA, I think this is rare - this is
relying on missing features of the spamming software ala greylisting.

But as Martijn says:
I think it's far more common than you think that a sending MTA isn't
listening on port 25.

I believe it's common for companies with large mail volume to separate
the inbound and outbound mail to different servers.  A result of that
may be that their outbound servers don't listen on port 25.

That said: have you done a feasibility study on this?  Have you tried
putting into your inbound SMTP server, recorded the results, and
analyzed them to determine the effectiveness and false-positive rate?

ietf-smtp mailing list